Update CONTRIBUTING.md
Update CONTRIBUTING.md

Separated document into sections, made some formatting changes, making text bold where required.
Added additional coding style guidelines
Added Section on PR's and Feature Branches
NumbersInternational/CefSharp,zhangjingpu/CefSharp,illfang/CefSharp,ruisebastiao/CefSharp,NumbersInternational/CefSharp,Haraguroicha/CefSharp,joshvera/CefSharp,wangzheng888520/CefSharp,Haraguroicha/CefSharp,rlmcneary2/CefSharp,ITGlobal/CefSharp,VioletLife/CefSharp,Haraguroicha/CefSharp,Haraguroicha/CefSharp,wangzheng888520/CefSharp,gregmartinhtc/CefSharp,AJDev77/CefSharp,yoder/CefSharp,gregmartinhtc/CefSharp,rover886/CefSharp,twxstar/CefSharp,Livit/CefSharp,illfang/CefSharp,VioletLife/CefSharp,dga711/CefSharp,rlmcneary2/CefSharp,rlmcneary2/CefSharp,wangzheng888520/CefSharp,haozhouxu/CefSharp,NumbersInternational/CefSharp,VioletLife/CefSharp,Octopus-ITSM/CefSharp,zhangjingpu/CefSharp,VioletLife/CefSharp,zhangjingpu/CefSharp,windygu/CefSharp,zhangjingpu/CefSharp,joshvera/CefSharp,joshvera/CefSharp,ITGlobal/CefSharp,AJDev77/CefSharp,wangzheng888520/CefSharp,rover886/CefSharp,battewr/CefSharp,battewr/CefSharp,Livit/CefSharp,AJDev77/CefSharp,battewr/CefSharp,windygu/CefSharp,ruisebastiao/CefSharp,yoder/CefSharp,ruisebastiao/CefSharp,jamespearce2006/CefSharp,ITGlobal/CefSharp,dga711/CefSharp,ruisebastiao/CefSharp,Octopus-ITSM/CefSharp,jamespearce2006/CefSharp,dga711/CefSharp,illfang/CefSharp,dga711/CefSharp,rover886/CefSharp,haozhouxu/CefSharp,yoder/CefSharp,Octopus-ITSM/CefSharp,gregmartinhtc/CefSharp,twxstar/CefSharp,AJDev77/CefSharp,jamespearce2006/CefSharp,haozhouxu/CefSharp,jamespearce2006/CefSharp,haozhouxu/CefSharp,windygu/CefSharp,Octopus-ITSM/CefSharp,illfang/CefSharp,rlmcneary2/CefSharp,Livit/CefSharp,twxstar/CefSharp,NumbersInternational/CefSharp,windygu/CefSharp,yoder/CefSharp,rover886/CefSharp,battewr/CefSharp,joshvera/CefSharp,rover886/CefSharp,Livit/CefSharp,Haraguroicha/CefSharp,twxstar/CefSharp,ITGlobal/CefSharp,jamespearce2006/CefSharp,gregmartinhtc/CefSharp